1. Field of the Invention
The present invention relates to an optical head comprising mount materials onto which an optical element and an optical fiber array are fixed, more particularly to such optical heads including an angle formed between a light emitting/receiving face of the optical element and an inclined face of a mount material for fixing the optical fiber array.
2. Description of Related Art
A conventional optical head includes a mount material for fixing an optical element, such as a light receiving element or light emitting element and a mount material for fixing an optical fiber array to which an optical fiber is connected, and the optical fiber is optically connected to the optical element.
FIG. 3 shows an optical head having a conventional light emitting element. An LD array 10 is provided such that a plurality of laser diodes are transversely arranged. A mount material 30 is made of a AIN ceramics with high heat conductivity, metalization for soldering is applied to its surface, and a wiring, pattern 31 and a drive IC 35 bonded by an electrode of the LD array 10 and a wire 32 are arranged. The LD array 10 is fixed to the mount material 30 by means of soldering so that light emissions ejected from the LD array 10 are generally coincident with each other.
An optical fiber array 20 includes at least one V groove 23 provided on a support substrate 22 in order to position an optical fiber 21, and a plurality of optical fibers 21 are arranged to be housed in the V grooves 23. These optical fibers are covered with a cap substrate 24 from the top, and are fixed by sheet shaped soldering, thereby forming an integral block 25.
At a position between the optical fiber array 20 and the LD array 10 optically coupled with each other, a support substrate 22 is protruded on the top face of a mount body 40; a spacer portion 34 is extruded on the side face of the mount material 40, and the spacer portion 34 is bonded with the side face of the mount body 40. In addition, this optical head is sealed with air tightness in a package by leading out an optical fiber or lead wire, whereby a parallel light transmission module is provided. In addition, an end face 20a of the optical fiber 21, with which the LD array 10 is optically coupled, is positioned at an end face of a block 25, and is formed so as to be opposed to a light emission plane 10a of the mount material 30 having the LD array 10 mounted thereon.
Next, in order to directly emit light from a light emitting element to a large diameter end face of an optical fiber or to emit the light expanded or contacted by a lens, an interval between a light emission element required for fine adjustment and the end face of the optical fiber is spaced, adjusted, and fixed when a connection face between mounted materials fixed to each other is defined as a reference. This derives from light intensity in a direction orthogonal to an optical axis of an optical element for example, a laser diode and light intensity averaging between a plurality of fibers of the optical head after light axis alignment.
That is, the light intensity in a direction orthogonal to an optical axis of a laser diode draws a Gaussian curve shape when an optical axis is defined as a center axis. However, when a point orthogonal to the optical axis is spaced from a laser diode, a top of the curve is lowered, and the gradient is gentle. When the top of the curve is low, light intensity is lowered. On the other hand, when the gradient is gentle, even if slight deviation from the optical axis occurs in a vertical direction, it indicates that a small rapid change occurs with light intensity.
In addition, in the optical head, even if the same optical intensity is input to a plurality of configured fibers, large deviation in light intensity must not be present between fibers due to deviation from the light axis.
The arrangement precision of a plurality of optical elements and the arrangement precision of a plurality of fibers must be permitted to some extent in view of manufacture. This means that another optical element and an optical fiber deviation from an optical axis even if an arbitrary optical element and the corresponding optical fiber are completely aligned with the axis. Even under such circumference, as means for preventing large deviation in light intensity between fibers, there has been conventionally performed means for spacing an optical element and an optical fiber from each other by a predetermined value. This method utilizes the fact that, although light intensity is lowered as deviation from an optical element is more significant as described above, the variation rate of light intensity in a direction vertical to an optical axis is gentle.
Specifically, a light emission element is fixed to a mount material by means of soldering; an optical fiber is pressed by from the top arranged and housed in a support substrate having a V groove punched thereon, and is fixed by means of soldering; and the support substrate is fixed to a top face of the mount material. At this time, when an end face of the mount material fixing an optical fiber array is defined as a reference face, the fixing position of the light emission element is adjusted by the mount material via a spacer for ensuring a design space. In addition, the position of a support substrate is fine adjusted while sensing the light receiving capability of an optical fiber fixed to the support substrate against the adjustment light from the light emission element.
However, in order to ensure this spacing distance, positional adjustment is cumbersome because it is intensively influenced by the dimensional precision of a spacer and the positional precision on the mount material for the light emission element. Thus, there has been a growing need for improvement of means capable of simplifying positional adjustment using check light by improving precision of adjustment technique utilizing a reference face of the mount material.
According to a first aspect of the present invention, there is provided an optical head including a mount material for fixing an optical element and a mount material for fixing an optical fiber array. The optical fiber is optically connected to the optical element. An angle formed between a light emission/receiving face of the optical element and an inclined face of the mount material for fixing the optical fiber array is 1 to 8 degrees. In this manner, an angle formed between a light emission/receiving face and an end face of an optical fiber is greater than 1 degree. Thus, noise produced by reflection light deriving from a light receiving face or an end face of an optical fiber opposed to a light emitting/receiving element is reduced as compared with a case in which the conventional light emission/receiving face and the end face of the optical fiber are substantially parallel to each other, and a failure with optical signal transmission can be prevented. In addition, an angle formed between the light emission/receiving face and an end face of the optical fiber is smaller than 8 degrees, and thus, bonding efficiency is improved. In addition, an end face can be shaved with high processing precision, and thus, the shaved portion can act as the above spacing distance. Therefore, the spacing distance can be ensured with high precision.
According to a second aspect of the present invention, there is provided an optical head wherein thermal expansion rates of the mount material of the optical element and the mount material of the optical fiber array are substantially equal to a thermal expansion rate of the optical fiber array material. In this manner, the thermal expansion rates of mount materials is substantially identical to each other. Thus, even if these materials are used under severe environments such that a temperature difference is large, there is no thermal contraction difference between the mount materials, and an axial deviation in optical signals fixed thereto and transmitted does not occur.
Further, according to a third embodiment of the present invention, there is provided an optical head wherein the optical fiber is a single mode, and the mount material of the optical element and the mount material of the optical fiber array are spot welded, such as Yag melded to each other. In this manner, a single mode optical fiber of 5 to 8 microns in core diameter is smaller in core portion diameter than a multiple mode optical fiber of 50 to 62.5 microns in diameter, the countdown dimensional precision up to sub-micron units can be precisely performed during adjustment. Moreover, the same kinds of mount materials are used. Thus, a thermal shrinkage difference is small, and an axial deviation in optical signals fixed thereto and transmitted does not occur.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.